A goal from sub Callum McCormack six minutes from time sealed victory for Westmeath in a foul-ridden game where Louth skipper Mark Brennan and free-taker Darren Clarke, along with Westmeath's John Heslin were dismissed.
Louth led by 0-7 to 0-5 at the interval but Westmeath pulled ahead with four points after the restart following the opening half dismissals of the Louth pair.
Louth managed to get back on level terms nine minutes from time before McCormack sealed it for Westmeath.
Louth had the strong wind behind them in the opening half but the dismissal of captain Mark Brennan and then sharpshooter Darren Clarke just before the break undermined their effort.
Louth had started well with a couple of early Clarke frees and a fine effort from Aaron Hoey and while Westmeath managed to level thanks to a brace of John Heslin frees and one from play by Ger Egan, Louth took control again.
But while they landed four points the dismissals greatly undermined their challenge and left them with an uphill task.
They still managed to lead by 0-07 to 0-05 at the interval but Westmeath took over after the restart and hit four without reply to edge in front.
Callum McCormack impressed after being introduced and it seemed as if Westmeath would pull away for a facile win.
But Louth worked very hard to overcome the numerical disadvantage and while another Egan point put Westmeath 0-11 to 0-8 in front after 50 minutes, it was Louth who took control.
Derek Crilly reduced the margin after 56 minutes and as Westmeath panicked, Ray Finnegan went forward for an excellent score before Jim McEneaney tied the match with nine minutes remaining.
But Westmeath regrouped and while they lost teenage midfielder Heslin to a second yellow, they struck for the decisive score six minutes from time.
The superb Ger Egan found Denis Glennon with a superb pass and he set up sub McCormack for a fine goal.
Westmeath pushed on from there and sealed their place in the next round as James Dolan, Egan, Denis Glennon and McCormack fired over late points for a rather flattering win in the end.
SCORERS:
Westmeath: C McCormack 1-03; G Egan 0-04; J Heslin 0-04 (4fs); D Glennon 0-03 (1f); J Dolan 0-01.
Louth: D Clarke 0-04 (4fs); J McEneaney 0-03 (3f); D Crilly 0-01; R Finnegan 0-01; D Byrne 0-01; A Hoey 0-01; JP Rooney 0-01.
Westmeath: D Quinn; M McCallon, J Gaffney, K Maguire; D Harte, P Sharry, D McDermott (C McCormack, 35); J Heslin, P Bannon; K Martin, David Glennon, G Egan; M Ennis (D Corroon 48), J Dolan, Denis Glennon.
Louth: N Gallagher; P Rath, D Finnegan, G Hoey (D Collier, 53); R Finnegan (D McComish, 68), M Fanning (D O’Connor, 67), D Byrne; J McEneaney, M Brennan; A Reid, A Hoey (J Carr, 35), D Reid; D Crilly, JP Rooney (R Moore, 56), D Clarke.
Referee: D Fahy (Longford).
